The dimensions for a storm jib are really whatever you think they should be. A "storm jib" designed for a Cat27 Tall rig will be fine for a Cat 27 Std rig, albeit maybe with a little more sq. ft. of sail area. The idea is to reduce your headsail area to something that the boat can accept given the winds you expect tot experience; there are no required dimensions. I've seen storm jibs from handkerchiefs (maybe 50 sq ft) to maybe only 20-25% smaller than a a regular (100%) jib. On a std rig on the NorCal coast (at Pt Reyes I've seen 35 knots - double reef main and storm jib at this was OK) mine is about 70 sq ft. (18ft luff x 8 ft foot). I've only used it that one time, but I carry it always when I'm "outside".
